An object of the present invention is to provide a process whereby a cellular ceramic product, which can be referred to simply as "foamed glass", is produced in a continuous and economical manner in the form of elongate members, more particularly in the form of hollow elongate cylinders. In such form, the foamed glass product can be used as a structural member in a number of industries including the housing industry as a bearing member, in processing industries as conduit, for example, as sewer pipe, and, in a particular exemplification, as a telephone pole or power line to replace wood poles. Particularly in the last utility, it will be appreciated that increasing demand for wood by numerous industries has caused shortages in the supply of wooden poles. Because of the inherent properties of the wood selected for such poles, they are excellent support members for high tension power lines and power poles have been constructed varying in length from 25 feet to almost 100 feet and formed to bear horizontal loads ranging in weight from below 400 lbs. to in excess of 11,000 lbs. However, material shortages and the competing demands for wood make it desirable to provide a substitute material. Such a material should be readily available, easily formed in lengths up to 100 feet, be able to withstand a stress of 5,000-8,000 psi, be economical in comparison with the purchase cost and life cycle cost of wood, be attractive or be capable of being made attractive, be fireproof and be a good electrical insulator.
The present invention provides such a material in the form of foamed glass produced by a continuous process which enables a pole structure to be directly obtained. In this general form, any glass composition can be used with appropriate foaming agents. In preferred embodiments, further economies are obtained by utilizing fly ash as a glass base or as a filler. Fly ash (calcium alumino-silicate, containing iron) is generated from coal and usually considered a waste material so that its utilization provides an extremely economical product.
More specifically, a continuous process is provided for the manufacture of cellular ceramic product in which a foaming agent is added to a ceramic feed, the foaming agent requiring a temperature in excess of 500.degree. C. for activation. The process comprises transporting ceramic feed through a first kiln section and preheating it at a temperature of at least 500.degree. C., but lower than the foaming agent activation temperature. Thereafter, the ceramic feed is transported into a second kiln section and a mixture thereof with the foaming agent is heated to the activation temperature for a time sufficient to form the foamed ceramic. The foamed ceramic is then transported while it is at or above its softening point to a drawing kiln section from which it is gathered and formed into product. The process is continuous so that while a first amount of the ceramic feed is fed through the kiln sections it is followed by a second amount either as a separate batch or continuously in a stream. In the first case, the ceramic feed mixture is initially deposited in powder form on refractory plates which are conveyed through the kiln sections, and the process can be referred to as a "powder process". In the second case, the ceramic material and foaming agent are heated to melt together in a tank, and the process can be referred to as a "tank process". The powder process is particularly useful where it is desired to add the foaming agent directly to the ceramic feed whereas a tank process is particularly suitable for adding the foaming agent to the feed after preheating, i.e., after passage of the ceramic feed to the first kiln section. Additionally, as a result of thermal balances, the powder process is most suitable for the use of fly ash as a filler and a ceramic feed can be used containing about 1-30% by weight of fly ash. The tank process is particularly suitable for use of fly ash as the major component.
The product obtained is formed as an elongate member having a length of at least 10 feet and a width dimension of about 3-36 inches. Preferably, the elongate member is in hollow tubular form and is obtained by drawing the foamed ceramic, while soft, around and past a hollow mandrel while air is passed through the mandrel. Specifically, with a preheat temperature of about 500.degree.-750.degree. C. and an activation temperature of about 800.degree.-1200.degree. C., a foamed ceramic product is formed having a cellular structure of closed, elongate bubbles in which the bubbles have a diameter in the range of about 0.01 mm to about 1 cm and a length in the range of about 2 mm to about 5 cm, the volume of said bubbles constituting about 10% to about 90% of the volume of the foamed ceramic.